Lost a hen today, white leghorn, sudden and no explanation :(

Today while I was at work, my mom noticed my one leghorn was walking a very different. Almost like she was "scooting" around, almost walking on her knees... With her whole body stretched out parallel to the ground. Walking slowly. Within a few hours she found her behind the coop, and there was blood on her beak coming out of her mouth and breathing heavy. She went limp when she picked her up. She passed on about half hour after, after some "fluff" spells, might even be seizure like.

She was approx. 18 weeks old, not yet laying.

She was perfectly fine this morning. What might of happened to her? We only have four hens so this is quite sad